It is known in liquid paint systems to add a tinting agent to a finished base composition to achieve a final colored paint composition. This technology permits the preparation of a large array of liquid custom color paints that can be created from a small number of finished base compositions. In coating powder paint systems, the addition of a tinting agent to a coating powder base composition is more difficult and generally requires extrusion, grinding, or sieving to adequately mix the dry components. Otherwise, when a coating powder base and tinting agent are mixed, resultant coatings having poor flow, inconsistent color, and surface defects are obtained. It is believed that this well-recognized difficulty for coating powder systems is caused by low wetting properties of the coating powder base composition. Thus, it is a long standing problem in the coating powder industry to be able to produce coating powders that are capable of obtaining good quality coatings using the highly advantageous technique currently used for liquid paint systems.
Others have attempted to solve this significant, long-standing problem in the art with use of techniques that are distinct from that of the present invention. A more detailed description of such attempts is set forth below.
U.S. Pat. No. 5,856,378, granted to Ring et al., discloses a powder coating composition for providing a coating having certain appearance or performance attributes. The powder coating composition comprises composite particles that are agglomerates of individual particle components that have been fused or bonded together into composite particles which are air-fluidizable and do not break down under the mechanical and/or electrostatic forces encountered during their application to the substrate. The individual particulate components, present as discrete particles within the composites, comprise a first, solid, particulate component and one or more additional, solid, particulate components that differ from the first particulate component. Each particle of the first component comprises a solid polymeric binder system at least a portion of which is a resin in an amount sufficient to impart coatability to the composition. The particles of the additional components(s) containing at least one substance that provides, together with the first component, the certain appearance or performance attribute to the coating when processed into a coating with the first component, the identities, particle sizes and proportions of the components in the composition being selected such that, when the composition is applied to a substrate and heated to form a continuous coating, a coating having the certain appearance or performance attribute is formed.
U.S. Pat. No. 6,133,344, granted to Blatter et al., discloses a colored pulverulent coating composition comprising spherical particles having a mean particle size>40 um, in two or more different color tints. At least the particles of one tint are colored and the particles of the other tint may be colorless. The particles employed for the mixture each have a monomodal particle size distribution with a span (d90-d10/d50) of <2.5 and the pulverulent coating composition can be melted at temperatures<200° C. to form a continuous coating. The differences in color that stem from the different-colored particles are indistinguishable to the human eye in the cured coating.
U.S. Pat. No. 6,146,145, granted to Itakura et al., discloses a method of producing a color-matched powder coating. The method comprises providing a colored light-transmittable powder coating that is colored by a coloring agent and a colorless light-transmittable powder coating containing no coloring agent. A blending ratio is calculated of the colored powder coating and the colorless powder coating. The colored powder coating and the colorless powder coating are weighed on the basis of the calculating step. The powder coating is dry blended using a mixer.
U.S. Pat. No. 6,531,524, granted to Ring et al., discloses a powder coating composition comprising a film-forming polymeric component having a d(v,50) in the range of from 25 to 50 microns or a d(v,70) in the range of from 25 to 70 microns. The composition includes at least one appearance modifying additive and a further additive, which may be alumina, together with aluminium hydroxide, wax coated silica, or a combination thereof. Ring et al. does not appear to use a coating powder base composition having a viscosity from about 2 to about 85 Pa·s that may be subsequently mixed with a particulate organic pigment tinting agent.
EPO 0 845 507 A relates to mixing two or more powder coatings of different color to provide a cured coating of a homogenous hue. On the other hand, the claimed invention relates to mixing a base composition having a viscosity from about 2 to about 85 Pa·s with a particulate organic pigment-tinting agent.
U.S. Patent Publication No. US-2003-0181570, of Ladatto, published Sep. 25, 2003, entitled Coating Powder Compositions and Method and U.S. Patent Publication No. US-2003-0191230, of Ladatto, published Oct. 9, 2003, entitled Coating Powder Compositions and Method, both relate to coating powder compositions, methods for making such coating powders, and coatings made from such products. Applicant believes that such patent publications are more closely related to the present invention than the respective coating powders and manufacturing methods described in the three above-mentioned U.S. patents. The two U.S. patent publications are assigned to the assignee of the present patent application.
The two above-mentioned patent publications involve the production of coating powders by providing a base composition powder comprising a resin having a viscosity from about 2 to about 85 Pa·s (Pascal-seconds) and then mixing the base composition powder with either an inorganic tinting agent or an organic polymer soluble dye tinting agent to obtain a coating powder having a desired color. Inorganic tinting agents include mixed metal oxides, titanium dioxide, and hybrid organic-inorganic materials. Organic polymer soluble dyes are referred to as “solvent dyes” and include perinone colorants.
The present invention may be advantageously used with a wide variety of coating powder compositions including thermosetting, thermoplastic, radiation curable, and dual systems such as thermosetting/radiation curable and fluorocarbon polymer thermosetting systems. Once a base coating powder having sufficient wetting properties, as measured by viscosity, is produced, particles of a solid organic pigment-tinting agent are then mixed with such particulate base coating powder to produce a desired color. An important commercial advantage of the invention is that a base coating powder can be produced and then stored to await the final, color-producing mixing step. To be able to obtain a desired colored powder by simply mixing a base composition and an organic pigment permits pre-production of large quantities of the base composition and then the subsequent use of a portion of such base to obtain a desired color rather than having a single production run capable of producing only one color. Obviously, shorter production and delivery times are possible with the invention. Moreover, if a coating powder manufacturer is in the midst of a production run of a given color, the only alternative to being able to quickly produce a different color could be to interrupt the run, clean the equipment, and then produce the other color. Then the equipment would require cleaning once more to produce the balance of the first run. This substantial problem is improved with the present invention, although addressed by the two above-mentioned patent publications. The present invention and that of the two patent publications enable a wide variety of colored powders to be quickly produced and shipped to customers without interruption of the base composition production run. The present invention enables such production and shipment to be accomplished with increased efficiency.
While Applicant considers that the above-described coating powders and method of making such coating powders disclosed in the two patent publications successfully address the several long standing problems in the art that are mentioned above, Applicant believes that the coating powders, method of making such coating powders, and coatings made therefrom of the present application constitute a significant improvement. Such improvement is manifested by improved properties in the coating powder and resultant coated substrate, and by several processing advantages. Such improvement is achieved by the substitution of particulate solid organic pigment tinting agents for the inorganic tinting agents and organic polymer soluble dye-tinting agents described by the two patent publications. Such substitution results in a superior product that is quite distinct from that of the two patent applications. Increased simplicity in manufacture is also achieved by the present invention.
Several significant product advantages result from the use of organic pigment tinting agents rather than inorganic tinting agents. When organic pigment tinting agents are utilized instead of inorganic tinting agents, less coloring agent is required to obtain the same color in most instances. Secondly, organic pigment tinting agents have a lower specific gravity than inorganic tinting agents. Such lower specific gravity is more closely related to the specific gravity of the base composition than that of the inorganic tinting agents. When the inorganic tinting agents disclosed in the two patent publications are added to base compositions, there is a tendency for the inorganic tinting agent particles to float and segregate at the top of the base composition. Incorporation of the lower specific gravity organic pigment tinting agents results in a uniform distribution of the pigment throughout the cross section of the cured coating. Uniformity is a significant advantage when it is considered that when a coating containing an inorganic tinting agent becomes scratched to a depth below the area containing the segregated tinting agent, the scratch becomes noticeable because of the difference in color at the lower regions of the scratch and the surface. On the other hand, the same scratch depth would not show such difference in color if a coating containing organic pigment tinting agents were utilized because color uniformity is exhibited throughout the coating. Typically, organic pigment tinting agents are significantly smaller than inorganic pigment tinting agents, i.e., on the order of about five to about ten times smaller. In general, there are more pigment particles in one gram of organic pigment than in one gram of inorganic pigment. Thus, lesser quantities in terms of mass of organic pigment tinting agents need be added to the base composition to produce a given color. The ability to use organic pigments in addition to inorganic pigments in matching a given color increases the opportunity to formulate a color match that is not metameric. Metamerism is the characteristic where two colors match in one light source but not in another. In general, coatings made with organic pigments will exhibit less metamerism when the target color is made from organic pigments. Previous publications, where inorganic pigments were used exclusively, resulted in metameric color matches.
Significant processing advantages are achieved through the use of organic pigment tinting agents rather than inorganic tinting agents. Because clear, unpigmented base compositions may be utilized when organic pigment-tinting agents are subsequently added, the need for an array of colored base compositions is significantly reduced. On the other hand, clear base compositions are not normally as suitable when inorganic tinting agents are used because some inorganic tinting agents lack opacity. As mentioned previously, because organic pigment tinting agents are generally more opaque than inorganic tinting agents, organic pigment tinting agents constitute a more potent colorant. For example, when matching a dark gray color using inorganic tinting agents, a dark gray base would be mixed with inorganic tinting agents to create the desired color match. When using organic tinting agents, a clear base would be mixed with organic tinting agents to create the same dark gray color match. The use of a clear base in combination with organic tinting agents eliminates the need for the dark gray base as well as many other color bases. In general, the reason why organic pigments are useful in combination with a clear base and inorganic pigments are not as useful is that organic pigments contain more color strength and opacity at lower use levels than inorganic pigments.
Organic polymer soluble dyes that may be utilized as tinting agents are sold by Clariant under the trade names Sandoplast, Solvaperm, Hostasol, Estofil, and Polysynthren. Such materials are chemical compounds that impart coloration to polymeric coatings by way of solubility. Such compounds are different from pigments in that these dyes completely dissolve within the matrix of the resin system of the coating. Organic polymer soluble dyes such as disclosed in previously mentioned Patent Publication No. US-2004-0096669, may encounter compatibility problems with the base composition and result in a spotty, non-uniform appearance. No such problem exists with certain organic pigment-tinting agents. Moreover, when a clear coat is applied over a base coat containing organic polymer soluble dyes, such dyes tend to bleed because the dye is soluble. Most organic pigment tinting agents will not so bleed. Thus, if one were to provide a clear topcoat over a colored coating, bleeding problems of the colored coating into the clear topcoat would be encountered should organic polymer solvent dyes be utilized. Obviously, such problem would not exist with most organic pigment tinting agents.
The chemical family of organic polymer soluble dyes is referred to as “solvent dyes”. The red dye, e.g. Sandoplast Red G, is known as perinone colorant (syn: Solvent Red 135, CAS #20749-68). Examples of such solvent dyes include, but are not limited to, Sandoplast Red G, Sandoplast Red BB, Polysynthren Blue, and Polysynthren Green.